second time trying to post this q.

Can I have 2 antennas in the attic, side by side, feeding 2 TVs?

My orig question
http://www.digitalhome.ca/forum/showthread.php?p=875866#post875866

As long as they're spaced enough apart to not affect each other, I don't see why not.
But a preamp + splitter would probably work just as well.

Can I have 2 antennas in the attic, side by side, feeding 2 TVs?If you go the 2 antenna route make sure to read Post #16 in the OTA FAQ for imporant info and tips.

hey does anyone like the winegaurd ap4700 , it was 80 bucks and has 19 db uhf gain and no vhf gain, but I think only 1 digital channel is in VHF in my area , so was this a good buy or should I have gotten the Titan. This is for the channels Master 4221HD.

I used an AP4700 for the past few years for experimenting and it has been excellent. If you look at the chart in Post #1 of this thread you can see that it is comparable to most commercial preamps for noise figure, and its gain is rated at 19dB. While it is a UHF-only preamp, it does not block out VHF, it just doesn't show any gain on it.

Hi all,

After doing some more research using the IC data on Stampeder's site, I've concluded that if you have anything over 0dB gain, the CM7777 is probably not the ideal preamp for you if you live in the GTA. My recommendations are based on a distance of approximately 36km from the CN Tower and 0dB antenna gain. If you're closer to the tower, or have >0dB antenna gain (including balun and antenna-to-preamp cable loss), the negatives of the CM7777 are even more exacerbated. Here is my reasoning:

1) During pre-transition (ie. now), we have some powerful analog stations, notably CFMT at 1138kW and TVO(CICA) at a whopping 1738kW, plus a handful of others at around 300kW, 500kW, and 700kW. As a result, at 36km from the tower, and 0dB antenna gain, the two powerful transmitters are around -32dBm and -30dBm respectively, according to loss calculations from tvfool.com and adjusted for actual ERP (instead of the max ERP value that tvfool typically [erroneously] uses). The CM7777 has a max input power (according to stampeder's/holl_ands' preamp chart) of -35.8dBm before intermodulation distortion (IMD) starts to play a significant role. IMD can reduce your ability to receive lower-powered (in our case, the US network) channels. That's not to say it *will*, but why chance it?

2) Post-transition (ie. Aug 2011, when analog goes off-air but digital channels potentially ramp-up their power output). Again using the same data, after the Canadian transition, we'll have CJMT (OMNI2) at 1000kW (approx -33dBm at my location) and other channels will be 100kW (~-43dBm at my location) or lower. Since IMD needs two or more strong signals to play a factor, the post-transition period will be more forgiving.

So what to do? If you're in the market for a preamp before August 2011 and you fit the description I provide (<= than my distance from the CN Tower and >= 0dB antenna gain in the direction of the tower), I'd recommend a preamp with a higher max input level. Personally, I'm now leaning towards something like a Winegard 8780 (max -28.8dB input power). After the transition it won't matter as much and the CM7777 may be superior. In the meantime, however, based on a typical scenario (1.5dB balun loss, 10dB post-preamp system loss, 6dB receiver noise figure), you're only losing about 0.6dB total system noise figure with a 8780 (per my cascaded noise figure calculation spreadsheet posted earlier) but potentially eliminating negative effects of IMD. Long story short? You may be able to receive more channels (or receive your current channels with more signal integrity) with a higher max-input-power preamp like a 8780 than with a CM7777.

I welcome your thoughts!
Tom

I've concluded that if you have anything over 0dB gain, the CM7777 is probably not the ideal preamp for you if you live in the GTA

Yep, overkill is never a good idea. Balance is the key.

Just a tip that tczernec's spreadsheet for calculating your OTA system's signal loss is now linked from Post #1 in this thread for easier finding, along with the Preamp Chart by holl_ands.

To use it, make sure to download it rather than using it online. ;)

cheers

Neat.. If I had known I'd get hooked on this OTA stuff so much, I would've chosen a username that rolls off the tongue/keyboard a little easier than 'tczernec'. A stretch maybe, but any way to change that short of creating a new account?

My Ukrainian grandmother would be proud of you for that username! :D

As would my Polish grandma :) Ok I'm straying this thread off-topic, so I'll stop :)

I have two antennas, top one is aimed to BUF and bottom TO. Can I put the 7777 before the joiner (right below the top antenna)?

I want amplification only for the BUF antenna, the TO stations are fine.

It should work fine, goforit. :)

I have two antennas, top one is aimed to BUF and bottom TO. Can I put the 7777 before the joiner (right below the top antenna)?

Just make sure that if the signal combiner is between the pre-amp and the power injector, that it will pass the DC power (not all will) and that the port that does pass the power is connected to the pre-amp.

Hello,

I've got a an external CM-4221 that I mounted about 3 weeks ago. ~80' of cable with two joints in between (surge arestor and coupler at distribution panel).

I'm getting ABC/NBC great, but CBS is coming in weak and I don't get MyTV at all.

When I put a splitter in the mix to fan out to an additional 2 TV's, I lose all Buffallo channels. I've tried a distribution amp (CM-3042) with no success (it improved the analog reception but the digitals couldn't lock).

I believe I have a few options as my next step:

Upgrade to a 4228, add another 4221 or try a pre-amp.

I'm leaning towards the pre-amp given that I want to fan out eventually to 2 TV's and 2 Tuner cards.

I'm concerned that a pre-amp may get overloaded given my close proximity to the CN-Tower. But I'm also concerned if I go too low it may not amplify the signal enough given that the distribution amp didn't do anything -granted that may be due to the high SNR.

Here's my TV-Fool profile:

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d7c72bb6bd97b4a

I'm debating between the Winegard HDP-269 or the CM-7777

Can someone point me to the Overload spreadsheet? I've seen it mentioned but can't seem to find it. Also, am I calculating the signal gain correctly? is it simply the NM minus the Signal? in my case this would put 8 channels above 0dB.

Thanks for any advice.

- Colin

Quite interesting that you can get NBC/ABC but not CBS, since CBS is a more powerful station. I assume you have already played with the pointing of the antenna to make sure it is pointed straight towards Buffalo rather than the CN Tower (though from your location they would be very close..)?

Other than that, the fact that a splitter makes you lose your other channels seems to point to you being right on the edge with respect to reception, so a preamp definitely seems to be the way to go (plus, a CM4228 is barely any better than a CM4221, contrary to what should be the case).

Not sure which overload spreadsheet you're referring to, perhaps the preamp list? That's in post #1 of this thread. Holl_ands also has a more detailed spreadsheet which you can use to derive the numbers in post #1, though it's quite technical and I have to admit I have not mastered the detail behind it.

Now on to overload -> although tvfool is reasonably accurate and uses the correct transmit power values for US stations, this is not the case for Canadian stations, where it uses the maximum possible power output rather than the actual power the station is transmitting. As a result, the output power listed on your tvfool report is deceiving because it makes the Canadian stations look more powerful than they are. The worst offenders in the GTA currently are actually analog channel 19 (TVO) transmitting at 1738kW and analog 47 (OMNI/CFMT) transmitting at 1138kW (a preamp doesn't care if it's digital or analog when it comes to generating nasties at overload conditions). In contrast, the most powerful digital station is CBC at a relatively lowly 38kW. Armed with this information, I calculate your received power for TVO and CFMT are:

Ch 19 TVO: -18.2dBm
Ch 47 CFMT: -22.5dBm

Since you're aiming almost right at the CN Tower to get to Buffalo, you're probably hitting another 10dB of gain on your antenna, making the values above -8.2dBm and -12.5dBm respectively. I would definitely go with the HDP-269 in your case, which has a maximum 'clean' input power level of -14.6dBm. You could tweak its performance even more by inserting an attenuator or extra splitter (3dB loss) between the antenna and the preamp to ensure you're not overloading the preamp. Unfortunately, overload in a preamp usually doesn't affect your high power channels, but it can make your low power channels (like the US stations) even worse.

So long story short, get the HDP-269, and if needed add additional attenuation before the input to ensure you're not overloading it.

Once the high power analog stations are shut off in August 2011, you should be able to remove any additional attenuation you added to give you even more performance (as long as we don't all of a sudden have all the digitals decide to transmit at 1MW, though that's quite improbable). Or you could at that point change to a preamp with higher gain and a lower maximum input spec. But until then, stick with the HDP-269 to be safe.

Hope that helps; let us know how it goes.
Tom

Hi Tom,

Thanks for the info, I'm going to get up on the roof again tomorrow and play with the adjustments of the antenna. I've done it a few times already and my results have been somewhat consistent.

I agree and was surprised that NBC is my strongest channel over ABC and CBS. (it's contrary to what most have experienced). The angle between the CN Tower and Buffallo is only about 15 degrees so there's not a lot of room for error. I also do not have a clear line of site (at least as far as I can tell) of the CN Tower.

The spreadsheet I was looking for is what another poster referenced in the following screenshot: http://s638.photobucket.com/albums/uu110/stanicet/amp/?action=view&current=amp-1-1.png&t=1237129616655

I'm going to attempt to raise the antenna another foot tomorrow and see if that helps and will look towards ordering the HDP-269 this week. Thanks for the tip. I guess my only concern with it, is it doesn't really offer that much more gain/SNR then the distribution amp I tried.

Do pre-amps function that much differently then distribution amps? At one point I tried putting the distribution amp outside where my lightening arrestor was to improve quality but that didn't help much. In fact when I tried it without the spliter it made things worse which is what concerns me most in that the pre-amp may harm my signal and not improve it.

Preamp Spec Summary and Overload Calculators are found here:
http://imageevent.com/holl_ands/files

Your signals levels are WAY TOO HIGH for hi-gain CM7777 per post-transition data.
Someone would need to re-calculate with ACTUAL Xmit power to check CURRENT levels.
For example, if actual power is half what TVFool (i.e. FCC dBase) presumes, reduce by 3 dB.

You could try a low-gain, high overload Preamp, but NO Preamp might be better.

Is it possible with the switch to Chinese production that some CM products are defective? I got a 7778 that's over a year old and it works great on my 4228HD. I recently bought a 7777 to go with my 4221HD and it made things worse. These are separate lines to separate TVs. Funny thing is the 7777 improved the analog signals, but made the digital signals worse (as I mentioned), I lost several stations that were easily picked w/o the amp; and very close stations were fine (overload was not a problem).

Do pre-amps function that much differently then distribution amps? At one point I tried putting the distribution amp outside where my lightening arrestor was to improve quality but that didn't help much. In fact when I tried it without the spliter it made things worse which is what concerns me most in that the pre-amp may harm my signal and not improve it.

Preamps are designed with lower noise figure in mind. They are installed near the antenna such that their high gain and low noise figure helps to reduce the overall system noise figure of your receiver chain. Distribution amps will have higher noise figures and are more useful in overcoming splitter losses that come into play if you want to split the signal to other tv's. However, a decent preamp will be able to overcome downstream splitting losses to some degree as well. Even the HDP-269 should do a decent job of lowering your system noise figure (degradation of signal to noise ratio between the antenna and the receiver) by as much as 10dB or more (depending on your other system factors). You can check it out for yourself with my system noise figure calculator here: http://spreadsheets.google.com/ccc?key=phsRNZNCpKqgbqKCH6hFmLw&hl=en

Tom